Here's what the ACLU says:

https://www.aclu.org/news/privacy-technology/can-border-agen...

I think the 48h detention is across the board (without a judge involved, border or not the border). ACLU says device seizure is up to 5 days barring "extenuating circumstances", whatever that means.

The same article says they can fairly arbitrarily do repeated 7-day extensions. And:

> We’ve received reports of phones being held for weeks or even months.